Technical Area of the Invention
The invention relates to a pipe, in particular configured as a chromatography column, for example a high performance liquid chromatography column, which has a metal casing with an inlay. Furthermore, the invention relates to a connection element for connecting a pipe of this type to a feed or discharge line. The invention also relates to a connection system or low and high pressure system, in particular configured as a chromatography system, especially, for example, a high pressure liquid chromatography system, comprising at least one pipe of this type and optionally a connection element of this type. The invention furthermore relates to a connection for a capillary system, in particular an HPLC system, containing a plastics material pressed body with a through-opening.
Prior Art
High performance liquid chromatography (HPLC) is an established method for the chemical analysis and separation of substance mixtures. The method belongs to the standard equipment of a laboratory in research and industry. In particular, this method tends to be used for in-vitro diagnostics. The basic principle is based on the different adherence energy of substances to be separated on a known substrate. For analysis, a substance mixture is brought into solution in a so-called mobile phase and the solution is then pressed at high pressure through a column of porous particles (stationary phase). Depending on the adsorption behaviour of the various substances on the stationary phase, the constituents of the substance mixture leave the separation column one after the other.
There is a need in the area of HPLC and, quite particularly, for HPLC applications in the area of in-vitro diagnostics, for bio-inert HPLC hardware. At no point of the HPLC apparatus is an ion exchange to take place between a metal part and the sample to be analysed by chromatography. Substance adherences, such as, for example, of proteins, or carry-overs are also to be avoided. Pipe systems which are, in particular, inert and low in carry-overs would therefore be desirable.
It has attempted, on the one hand, to solve these problems in that, for example, high-grade steel pipes were inertly coated on the inside or were provided with glass inlays. On the other hand, in the HPLC area, complete systems are generally used nowadays, containing columns, screw connections, frits and capillaries, which are manufactured completely from plastics material, in particular polyetheretherketone (PEEK).
The following drawbacks are produced from using pure plastics material column systems:
Only low pressures can be applied to the system for packing the column or for transportation of the sample through the column, as well as low operating pressures. Thus relatively long passage times of the sample result.
Frequently desired micro columns are not possible, or only possible to a limited extent, because of the higher pressures required.
Only pure PEEK columns are generally commercially available. Although frequently required so-called PEEKsil columns (composite of glass pipe encased by PEEK) are available, their connection generally has to firstly be adapted, which often causes problems for the user.
The threads are often relatively weak because of the material properties of the PEEK and can only withstand a correspondingly low torque.
The commercially available PEEK columns are expensive, as they are produced by a complex centrifugal method.
The column dimensions have to have a specific size (standard). Deviations mean high tool costs.
The following drawbacks are produced by using coated systems (coated high-grade steel):
The production of a gap-free coating is difficult; in particular it is not practicable to prove a gap-free coating over the complete internal diameter of the system. Consequently there is no process reliability.
With a different layer thickness, metal ions can diffuse into the sample at the points at which the coating is too thin.
The sealing at the end face or the transition between the coated pipe and connection fitting is not ideally solved.
The following drawbacks are produced from the use of glass inlay columns:
Glass inlay can easily break or rupture and can therefore become untight.
There is generally a gap between the glass inlay and high-grade steel and this leads to a break at elevated pressure. High pressures can therefore not be applied.
The sealing at the end face or the transition between the HPLC column with the glass inlay and connection fitting is not yet ideally solved.
The published application WO 2011/076244 A1 relates to an assembly element for a fluidics device, in particular for applications in devices for high performance liquid chromatography. An assembly element of a fluid coupling for coupling a pipeline to a fluidics device is disclosed. The assembly element contains a pipeline with an inlay, the inlay being located in a cavity of a front side of the pipeline and projecting slightly out of the line. The inlay is used for sealing during coupling to a chromatography device. The pipeline, depending on the application, may have a plastics material (for example PEEK) on the inside. The drawback here is, in particular, that the connection takes place upon coupling over said inlay so that not only one joint is produced but simultaneously two joints between the pipeline and its coupling partner. Each additional connection point harbours the danger of contamination and carry-over of impurities. In addition—depending on the embodiment of the pipe—the effective connection face of the insert and innermost pipeline layer is optionally very small, which additionally reduces the reliability of the coupling system.
The published application EP 2 315 022 A1 shows a chromatography column with a frit ring, frit holder and end connection. The sealing of this system extends over a plurality of joint connections between the pipe and frit ring, frit ring and frit holder as well as frit holder and end connection. With this structure, the numerous connection points (joint points) being produced during the coupling, are problematical with regard to a carry-over of impurities and contamination.
A biocompatible liquid chromatography column is described in the U.S. Pat. No. 5,736,036. The inner pipe of the column is integral and can therefore not be pulled through the outer pipe or separated. An axial slipping of the inner pipe relative to the outer pipe is thus ruled out. In terms of manufacturing, restrictions are imposed by this structure. In particular, the inner pipe is introduced by a casting method. During casting, a material-uniting connection is formed between the outer and inner pipe. The drawback in the casting method are the increased manufacturing costs, which in particular also arise in that with the desired thickness variation of the inner pipe, the latter cannot easily be exchanged, but the column in each case has to be manufactured in various configurations. The outlay to produce various combinations of inlay thicknesses and column lengths and to have them in stock correspondingly has to be rated as high. In addition, because of the cast manufacturing, bubbles may form, which reduce the effective wall thickness of the inner pipe. In addition, checking for bubbles is difficult in the completed pipe composite.